On BarelyFitz Designs, there's a handy tutorial that's been posted to help developers out there combine the powers of PHP and CSS to form a sort of color management system for their site.

While many web sites use powerful programming environments to create HTML, these same tools are usually ignored when it comes to creating Cascading Style Sheets (CSS). This article describes how to take control of your colors in CSS using PHP. You will learn how to:

Centralize your color definitions using variables.

Separate presentation and content by referring to colors using abstract names such as base and highlight.

Automatically generate a color gradient from a single base color:

Automatically adjust the contrast of foreground colors so they can viewed on top of your background colors

They follow the steps to making a CSS file with PHP - generate the header and output the CSS - as well as examples of its usage. They create a range of colors based around a central one, five levels in either direction. The file they've created to accomplish this is also available for download.